[2020-12-09] Add solutions for day09

Makefile

@@ -27,6 +27,8 @@ day08:
 	go run main.go day08 input
 
 day09:
+	go run main.go day09 input
+
 day10:
 day11:
 day12:

day09/example.txt

@@ -0,0 +1,20 @@
+35
+20
+15
+25
+47
+40
+62
+55
+65
+95
+102
+117
+150
+182
+127
+219
+299
+277
+309
+576

day09/lib.go

@@ -0,0 +1,41 @@
+package day09
+
+import (
+	"sort"
+)
+
+func isSumOfPreviousNumbers(current int, previous []int) bool {
+	for _, n1 := range previous {
+		for _, n2 := range previous {
+			if n1+n2 == current {
+				return true
+			}
+		}
+	}
+
+	return false
+}
+
+func findAnomalySum(anomaly int, numbers []int) int {
+	for k1 := range numbers {
+		sum := 0
+
+		for k2, n2 := range numbers[k1:] {
+			sum += n2
+
+			if sum > anomaly {
+				break
+			}
+
+			if sum == anomaly {
+				targetSet := numbers[k1 : k1+k2+1]
+
+				sort.Ints(targetSet)
+
+				return targetSet[0] + targetSet[len(targetSet)-1]
+			}
+		}
+	}
+
+	return 0
+}

day09/parse.go

@@ -0,0 +1,22 @@
+package day09
+
+import (
+	"strconv"
+
+	"git.elis.nu/etu/aoc2020/utils"
+)
+
+var rows []int
+
+func ParseFile(input string) {
+	// Parse file
+	for _, line := range utils.GetLinesFromFile("day09/" + input + ".txt") {
+		number, err := strconv.Atoi(line)
+
+		if err != nil {
+			continue
+		}
+
+		rows = append(rows, number)
+	}
+}

day09/solve1.go

@@ -0,0 +1,26 @@
+package day09
+
+import (
+	"log"
+)
+
+func Solve1() {
+	anomaly := 0
+
+	rangeSize := 25
+
+	if len(rows) == 20 {
+		rangeSize = 5
+	}
+
+	i := 0
+	for _, num := range rows[rangeSize:] {
+		if isSumOfPreviousNumbers(num, rows[i:i+rangeSize]) == false {
+			anomaly = num
+		}
+
+		i++
+	}
+
+	log.Printf("2020-12-09.01: Answer: %d\n", anomaly)
+}

day09/solve2.go

@@ -0,0 +1,25 @@
+package day09
+
+import (
+	"log"
+)
+
+func Solve2() {
+	anomaly := 0
+
+	rangeSize := 25
+	if len(rows) == 20 {
+		rangeSize = 5
+	}
+
+	i := 0
+	for _, num := range rows[rangeSize:] {
+		if isSumOfPreviousNumbers(num, rows[i:i+rangeSize]) == false {
+			anomaly = num
+		}
+
+		i++
+	}
+
+	log.Printf("2020-12-09.02: Answer: %d\n", findAnomalySum(anomaly, rows))
+}

main.go

@@ -12,6 +12,7 @@ import (
 	"git.elis.nu/etu/aoc2020/day06"
 	"git.elis.nu/etu/aoc2020/day07"
 	"git.elis.nu/etu/aoc2020/day08"
+	"git.elis.nu/etu/aoc2020/day09"
 	"git.elis.nu/etu/aoc2020/utils"
 )
 
@@ -44,5 +45,8 @@ func main() {
 
 	case "day08":
 		utils.Perf("2020-12-08", day08.ParseFile, day08.Solve1, day08.Solve2)
+
+	case "day09":
+		utils.Perf("2020-12-09", day09.ParseFile, day09.Solve1, day09.Solve2)
 	}
 }